1. Technical Field
This invention relates to the design of internal combustion engine housings including its constituent components such as a cylinder block, crankcase, and oil pan, and more particularly to the technology of reducing the weight of such components without affecting their operating integrity and doing so at a reduced manufacturing cost.
2. Discussion of the Prior Art
The possibility of making an internal combustion engine out of Polymeric materials has been considered for some time but has been constrained mostly to speculation and research Prototypes A fiber-reinforced plastic engine housing would reduce vehicle fuel consumption directly through its weight reduction and indirectly through the weight reduction of associated components. Manufacturing costs would be reduced by minimizing the size and weight of metal components, increasing the number of units cast in each mold box, shortening the time to produce the component, increasing corrosion resistance, reduction of scrap, and by the reduction of subsequent external machining and finishing costs. The noise, vibration, and harshness (NVH) of the power unit would be decreased by the inherent sound insulation (noise damping) properties of fiber-reinforced materials. Additionally, time taken for the engine to warm up from a cold condition would be reduced because of the smaller metallic content of the engine and the reduction of heat loss.
In spite of these potential advantages, the use of fiber-reinforced plastics or phenolics must take into consideration that a modern spark ignition engine operates in a very harsh environment. The engine materials are subjected to oil and water/ethylene glycol at temperatures up to 400.degree. K., exhaust gases at mean temperatures up to 1100.degree. K., and peak temperatures in the combustion chamber of 2400.degree. K. while under conditions of high stress on the order of 200 MPa. Under these conditions, an engine is expected to also have a long life with minimal wear and be able to withstand excessive under-bonnet temperatures during "hot soak".
The first initial use of plastics in engines has been with respect to rocker covers, thermostat housings, and timing chain or belt covers; the immediate vehicle environment for these types of components is much less harsh and therefore excellent creep properties are not essential for these components. When attention is focused on the engine block and cylinder head assembly, the immediate environment is much more demanding and challenging because the structure must sustain the combustion pressure and convert it to mechanical torque at the crankshaft. The reaction of this torque is transmitted through the base block structure to both the transmission housing and engine mount and ultimately to the vehicle structure.
Due to the necessity for withstanding torque and pressure, the next sequential prior art concept envisioned was for use of metallic insert cylinder bore sleeves accompanied by plastic as the outer sleeve or framework for the block; in all cases, the plastic and metallic members are bolted together to withstand torque and pressure (see U.S. Pat. Nos. 4,644,911; 4,726,334; and 4,446,827). The high compression loads that are constantly present at the liner and main bearing clamping points, resulting from bolting, will lead to creep of the composite material and eventual failure.
What is needed is a new approach to making a composite internal combustion engine housing that simplifies securement of the composite material without critically affecting its integrity and structural rigidity.